As an exhaust-gas purifying device for an internal combustion engine, there are known a particulate filter (hereinafter, referred to as a filter) which traps particulate matters (hereinafter, referred to as PM) in exhaust-gases and a NOx storage reduction catalyst which reduces and purifies nitrogen compounds (hereinafter, referred to as NOx) in exhaust-gases.
These filters and NOx storage reduction catalyst need a periodic regenerating operation for restoring the purification capacity thereof. A general regenerating operation involves supplying unburned fuel by post injection to an oxidation catalyst which is disposed upstream of these filters and the NOx storage reduction catalyst and increasing the exhaust-gas temperature to a high temperature necessary for regeneration by means of heat of oxidizing reaction (for example, refer to Patent Literature 1).